This invention relates generally to the field of laryngeal prostheses. In particular, it relates to a laryngeal prosthesis which can discriminate between an exhalation effort and a phonation effort, in a manner analogous to the natural larynx.
The larynx performs two functions. First, it contains the vocal chords, by means of which vocal sounds are produced. Of equal importance, the larynx includes a movable tissue, the epiglottis, which prevents food and liquids from entering the trachea from the mouth.
Disease or injury may require the removal of the larynx by a surgical procedure known as a laryngectomy. As a result of the laryngectomy, the patient is left with an opening, or tracheostoma, directly into the trachea from the front of the neck, and the patient can then exhale and inhale through the tracheostoma. Because the epiglottis is also removed, a barrier or "pseudoglottis" between the pharynx and the trachea is provided by suturing the tracheal-esophageal wall to the interior tissue of the neck, covering the normal tracheal opening into the hypopharyngeal cavity.
The laryngectomized patient is thus left without the usual means to produce speech. In some patients, the speech function can be restored by a technique known as esophageal speech. This technique is difficult to master, and is, therefore, of benefit only to the minority of patients who can successfully learn it. Even so, the sound produced is not altogether natural.
Consequently, efforts have been made to produce an artificial larynx, or laryngeal prosthesis, to provide a speech function more closely approaching that of the natural larynx. In this regard, several approaches have been taken.
One common approach may be generally termed the "external laryngeal prosthesis." Typically, such a prosthesis includes a valve assembly, mounted external to the tracheostoma, which allows normal breathing therethrough. For speaking, such devices include means for diverting air into the lower regions of the vocal tract, such as the hypopharyngeal cavity, in the vicinity of the area formerly occupied by the larynx. This diverted air flow can be used to form vocalized sounds, frequently with the aid of a vibrating membrane or reed.
Examples of such prior art devices are shown in U.S. Pat. No. 3,747,127 to Taub; U.S. Pat. No. 3,952,335 to Sorce et al.; U.S. Pat. No. 4,060,856 to Edwards, and U.S. Pat. No. 4,223,411 to Schoendorfer et al.
One drawback to such devices is the need to provide a second surgical opening, or fistula, in the neck in order to direct the diverted air flow for speech around the surgically formed "pseudoglottis" mentioned above. While the surgical procedures used to form such fistulas are, more or less, routine, any additional surgery is, preferably, to be avoided, if possible.
Another disadvantage to such devices resides in the means used to discriminate between normal exhalation and a speech effort. For example, one class of external laryngeal prostheses, represented by a device disclosed in the above-referenced Edwards patent, requires the manual actuation of a valve which diverts air into the hypopharyngeal area when speech is desired. Such a mechanism is awkward to use, and it may be inoperable by patients with impaired use of their arms and hands.
Alternatively, devices such as those disclosed in the Taub, Sorce et al., and Schoendorfer et al. patents incorporate a pressure-discriminating mechanism which automatically distinguishes between a normal breathing effort and a speech effort. For example, the Schoendorfer et al. device uses a vibratory tone-generating mechanism which vibrates only when the user exhales above a preselected pressure, so that normal exhalation occurs silently. This device has no provision for allowing coughing or heavy breathing (as from physical exertion) without actuating the tone-generating mechanism. The Taub device uses a valve which normally opens a passageway for exhalation, but which closes the passageway in response to the increased pressure of a speech effort, so that exhaled air is diverted into an esophageal fistula for phonation via the esophageal mucosa. One drawback to the Taub device is that it does not allow the patient to cough freely or to breathe heavily without manual adjustment of the valve mechanism.
The Sorce et al. device uses a valve which allows exhalation through the tracheostoma at normal exhalation pressures and diverts exhaled air into the hypopharynx through a hypopharyngeal fistula at increased exhalation pressures indicative of a speech effort. The valve in this device allows the patient to cough freely by uncovering the normal exhalation passage through the tracheostoma in response to the high pressure generated by a cough. After a cough, however, the valve may require manual resetting to permit speech again. As with the Schoendorfer et al. device, sounds may be produced by heavy breathing, especially if a vibratory tone-generator is used.
From the foregoing discussion of the prior art, it can be seen that there is an as yet unfulfilled need for a laryngeal prosthesis which automatically discriminates between a normal breathing effort and a speech effort, and which allows the patient to cough freely, without the need for external manipulation either to select a mode of operation or to reset the device to an operable mode. In addition, there is a need for such a device which further discriminates automatically between a speech effort and a "heavy" breathing (gasping) effort, so that such heavy breathing is not accompanied by a tone. Moreover, there is lacking a device of this nature which is operable without an esophageal or hypopharyngeal fistula in addition to the tracheostoma. There is a further need for such a device which is simple of construction and relatively maintenance free. Finally, there is a need for a laryngeal prosthesis which not only includes the aforesaid features, but which also provides a suitable epiglottal function.